Temperature Thermistors - Bryant 189BNV EVOLUTION Service Manual

6
5
4
3
2
1
0
0 25 50 75
Pressure - Sealed Gauge (psi)
Fig. 35 – Suction Pressure Transducer (SPT)
Output Funtion Graph

Temperature Thermistors

Thermistors are electronic devices which sense temperature. As the
temperature increases, the resistance decreases.
thermistors are used to sense outdoor air temperature (OAT), coil
temperature (OCT) and the suction line temperature (OST) located
between the reversing valve and the accumulator. A 50Kohm
thermistor is used to sense discharge temperature (ODT).
Refer to Table 5 and Fig. 36 and 37 for resistance values versus
temperature.
Table 5—10K/50Kohm Resistance Values vs Temperature
10Kohm
_C (_F)
TEMPERATURE
25.0 (77.0)
0.0 (32.0)
-28.0 (-18.4)
50Kohm
125.0 (257.0)
75.0 (167.0)
25.0 (77.0)
THERMISTOR CURVE
90
80
70
60
50
40
30
20
10
0
0 20 40
TEMPERATURE (DEG. F)
Fig. 36 – 10K Thermistor Resistance Versus Temperature
50K THERMISTOR
450
400
350
300
250
200
150
100
50
0
0 20 40
TEMPERATURE (°
Fig. 37 – 50K Thermistor Resistance Versus Temperature
If the outdoor air or coil thermistor should fail, the control will
flash the appropriate fault code (see Table 6).
IMPORTANT: The outdoor air thermistor, coil thermistor and
suction thermistor should be factory mounted in the final locations.
100 125 150 175 200 225
A12035
10Kohm
RESISTANCE (ohms)
10.0 + / --- 2.3%
32.6 + / --- 3.2%
85.5 + / --- 3.4%
1.7 + / --- 1.6%
7.40 + / --- 2.0%
50.0 + / --- 2.3%
60 80 100 120
A91431
60 80 100 120
°
F)
A14022
Check to ensure thermistors are mounted properly (See Fig. 2,
3, 4, 5 and 6).
Thermistor Sensor Comparison
The control continuously monitors and compares the outdoor air
temperature sensor and outdoor coil temperature sensor to ensure
proper operating conditions. The comparison is:
S In cooling if the outdoor air sensor indicates  10_F ( 5.6_C)
warmer than the coil sensor (or) the outdoor air sensor indicates
 25_F ( 15_C) cooler than the coil sensor, the sensors are out
of range.
In heating if the outdoor air sensor indicates  35_F ( 19.4_C)
S
warmer than the coil sensor (or) the outdoor air sensor indicates
 10_F ( 5.6_C) cooler than the coil sensor, the sensors are out
of range.
If the sensors are out of range, the control will flash the appropriate
fault code as shown in Table 6.
Failed Thermistor Default Operation
Factory defaults have been provided in the event of failure of
outdoor air thermistor (OAT) and/or outdoor coil thermistor
(OCT).
If the OAT sensor should fail, defrost will be initiated based on coil
temperature and time.
If the OCT sensor should fail, defrost will occur at each time
interval during heating operation, but will terminate after 2
minutes.
If there is a thermistor out- -of- -range error, defrost will occur at
each time interval during heating operation, but will terminate after
2 minutes.
Count the number of short and long flashes to determine the
appropriate flash code. Fig. 38 and Table 6 gives possible causes
and actions related to each error.
Maximum Power Mode - - Inverter Over Temperature
The outdoor unit is equipped with inverter temperature sensing. If
the inverter senses a temperature above the high threshold limit it
will respond as follows:
1. Display the local fault code only on the AOC Status LED.
2. The system will continue to run but attempt to mitigate by
speed reduction.
3. When the system demand is satisfied, the unit will shut
down.
4. If the fault is still active on the AOC Status LED, the ODF
will continue to run at 500 RPM until the inverter
temperature falls below the threshold.
5. The compressor will not restart if the fault is still active.
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